Fortify Me—With Vitamin D!

“This is the new craze,” declared Vivian Nicholson in a voice that was part awe, part acerbic New York skepticism. “It was E for a long time, so now they’re going to go backward in the alphabet to D.”

Ms. Nicholson is a Montessori teacher, but she was not talking about the latest schoolyard fad. Rather it was vitamin D—formerly a shabby, stepsister supplement, now suddenly the belle of the nutrition ball—that was the topic of discussion. “Whenever I go to any social occasion, I’ll mention it just in passing … and somebody will invariably say, ‘Oh, my mother was told …’, or, ‘My daughter, my kids …’” she said. “It’s really spreading like wildfire.”

These days, doctors are doing it, socialites are doing it, even doctors who sometimes double as socialites are doing it.

“It just seems like there’s a lot of really great things that it does,” said Dr. Lisa Airan, the Upper East Side fashion plate and dermatologist who, in addition to taking a daily vitamin D supplement herself, has made a practice of testing her patients’ levels. “Everyone I see, I ask them if I can check it.”

‘I met somebody who was like, “I went on vitamin D, and I realized I’ve been a bitch for two years.”’—Mary Purdy, registered dietician

Vitamin D hasn’t always enjoyed this kind of Chosen One status. Until a few years ago, it was either overlooked as a kind of second-tier nutrient, the helpful Robin to calcium’s Batman, or disparaged as a fat-soluble vita-villain that, when taken as a supplement, could accumulate unhealthfully in the system.

But in recent years, research has given vitamin D a new identity. No longer feared, D is now being touted as the latest, greatest nutritional panacea, the cure-all capable of preventing, if not solving, all kinds of ailments, from breast cancer to the common cold to mood disorders.

“I met somebody—this wasn’t a patient of mine—who was like, ‘I went on vitamin D, and I realized I’ve been a bitch for two years,’” said Mary Purdy, a registered dietician and New York transplant to misty Seattle. “She was upset all the time, I mean all the time, just down all the time, and she started taking vitamin D, and it was a complete turnaround.”

Forget toxicity: These days the big fear is D-deficiency.

“Four hundred [international units] is out, and 1,000 is in. And now I have a 5,000 IU that sells quite a bit,” said Jason Bander, general manager and supplement buyer for Lifethyme Natural Market, a West Village health-nut hub that has experienced such a “steep curve” in vitamin D sales that it’s been wiped clean of its stock several times within the past 18 months. “But I have to admit, you’re also working with the New York hyperbole: ‘I need the highest, I need the most, I need the best!’

BUT EVEN OUTSIDE New York’s competitive precincts, vitamin D has become de rigueur. According to Quest Diagnostics, the demand for vitamin D serum testing has soared a hefty 50 percent during the past year; suppliers like Jarrow Formulas have seen sales double in less than two years. And as much as crazed, Suzanne Somers–style vitamin fiends might have helped fuel part of the binge, the story of vitamin D is about somehing fundamentally more 21st century.

In its best, most basic form, vitamin D comes from the sun. Cheerily known as the sunshine vitamin (even though it’s technically a hormone), it is made by the body when the sun’s UV rays seep into bare, sunscreen-less skin. But in these vampiric times, when sunlight is scorned as a skin-shriveling, cancer-causing demon and most people are too busy ass-bonding with their couch or computer chair to get outside much anyway, Americans just aren’t making as much of it. And some, like Ms. Nicholson, the Montessori teacher, are suffering some serious vitamin D-privation. Just this past spring, she was told that her vitamin D serum levels were a mere 7 nanograms per milliliter—dramatically lower than the 30 nanograms per milliliter that is considered to be the absolute low end for healthy adults.